The present invention relates to a sensing and/or measuring system of the type which operates to determine the position of at least one surface of a test object and which includes a housing, a receiving element fastened to the housing for securing the housing to a tool receptacle of a spindle, a sensing pin, a voltage source in the housing, and at least one measuring system responsive to the sensing pin and powered by the voltage source.
Such devices have been used in connection with coordinate measuring machines and with numerically controlled processing machines in order to determine the position and/or the dimensions of a test object, workpiece, or tool.
In West German DE-OS No. 28 40 934 there is described a sensing arrangement which includes a housing that is fastened to a tool receptacle of the spindle of a machine tool. A sensing pin projects from the bottom of the housing, and the sensing pin defines a sensing ball. The sensing pin is movably mounted in the bottom of the housing by means of a membrane, and the sensing pin is connected within the housing to a plate. The plate is pressed by means of a spring against the bottom of the housing and the plate is engaged with four measuring value transformers which register each deflection of the sensing pin in axial as well as radial directions. The output signals generated by these measuring value transformers are applied to a signal preparation circuit which is connected with a voltage source arranged within the sensing device. The signal preparation arrangement is switched on by a switch which is operated when the sensing ball is placed on a surface of the workpiece to be tested. The output signals of the signal preparation circuit are transmitted wirelessly to an external reproducing circuit. Since for the operation of the switch a relatively great axial displacement of the sensing pin is required, measuring precision is impaired. In addition, the switching reliability of the switch is dependent upon wear and the frequency of switching.
The publication "Maschinenmarkt", Wurzburg, 88 (1982) 68 at pages 1374 and 1375 describes a three-dimensional measuring sensor with a built-in voltage source in the form of an accumulator for optical signal transmission. It is only with the installation of the measuring sensor into the tool receptacle of the spindle of a machine tool that the accumulator is switched over from a standby mode with low current comsumption into a measuring mode. This is done in order to lengthen the life of the accumulator in response to an optical switch-on signal supplied by the machine tool. This optical arrangement for the switching on of the measuring sensor, because of the necessary components, is a relatively expensive approach. Furthermore, because the transmitter or the receiver may be optically blocked by contamination, and because foreign objects may inadvertently block in the beam path, this system is not foolproof. In addition, there is the possibility of a reciprocal interference with the machine with which the measuring sensor is used.